Segment Information Geographical Locations (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2015	Mar. 31, 2014	Mar. 31, 2013
Revenues from External Customers and Long-Lived Assets [Line Items]
Sales and Other Operating Revenues:	$ 738,097	$ 488,921	$ 589,815	$ 249,017	$ 615,839	$ 654,550	$ 700,680	$ 383,887	$ 2,065,850	$ 2,354,956	$ 2,243,816
Property, Plant and Equipment, Net:	237,975				261,246				237,975	261,246	270,978
United States [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Sales and Other Operating Revenues:									363,964	467,111	423,617
Property, Plant and Equipment, Net:	57,861				53,517				57,861	53,517	45,213
China [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Sales and Other Operating Revenues:									254,658	401,480	308,935
Belgium [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Sales and Other Operating Revenues:									137,513	125,377	185,668
Russia [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Sales and Other Operating Revenues:									118,233	125,093	147,283
Germany [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Sales and Other Operating Revenues:									116,713	130,163	93,990
Indonesia [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Sales and Other Operating Revenues:									58,609	58,919	109,983
Other [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Sales and Other Operating Revenues:									1,016,160	1,046,813	974,340
Property, Plant and Equipment, Net:	4,062				3,800				4,062	3,800	4,325
Brazil [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Property, Plant and Equipment, Net:	87,161				92,142				87,161	92,142	99,492
Malawi [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Property, Plant and Equipment, Net:	25,704				27,227				25,704	27,227	28,683
Tanzania [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Property, Plant and Equipment, Net:	23,610				24,979				23,610	24,979	24,568
Europe [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Property, Plant and Equipment, Net:	15,191				19,711				15,191	19,711	20,370
Argentina [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Property, Plant and Equipment, Net:	7,390				7,325				7,390	7,325	7,909
Asia [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Property, Plant and Equipment, Net:	6,960				7,545				6,960	7,545	8,436
Zambia [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Property, Plant and Equipment, Net:	6,582				6,690				6,582	6,690	6,316
Turkey [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Property, Plant and Equipment, Net:	$ 3,454				$ 18,310				$ 3,454	$ 18,310	$ 25,666