Property, Plant, and Equipment (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Jun. 30, 2013
Property, plant and equipment, net [Abstract]
Property, plant, and equipment, gross	$ 581,816		$ 574,701
Less accumulated depreciation, depletion and amortization	(163,742)		(152,254)
Property, plant, and equipment, net of accumulated depreciation, depletion and amortization	418,074		422,447
Depreciation [Abstract]
Depreciation, depletion and amortization	11,287	11,683
Depreciation, depletion and amortization expense recorded in cost of goods sold	11,018	11,502
Depreciation, depletion and amortization expense recorded in selling, general and administrative expenses	269	181
Capitalized interest	0	0
Land, Land Improvements, and Land Use Rights [Member]
Property, plant and equipment, net [Abstract]
Property, plant, and equipment, gross	9,125		9,085
Building and Improvements [Member]
Property, plant and equipment, net [Abstract]
Property, plant, and equipment, gross	88,234		87,486
Machinery and Equipment [Member]
Property, plant and equipment, net [Abstract]
Property, plant, and equipment, gross	200,839		196,915
Furnaces [Member]
Property, plant and equipment, net [Abstract]
Property, plant, and equipment, gross	204,059		202,444
Mineral Reserves [Member]
Property, plant and equipment, net [Abstract]
Property, plant, and equipment, gross	55,843		55,843
Mine Development [Member]
Property, plant and equipment, net [Abstract]
Property, plant, and equipment, gross	4,863		4,863
Other [Member]
Property, plant and equipment, net [Abstract]
Property, plant, and equipment, gross	11,842		11,279
Construction in Progress [Member]
Property, plant and equipment, net [Abstract]
Property, plant, and equipment, gross	$ 7,011		$ 6,786