Property, Plant and Equipment - Schedule of Property, Plant and Equipment (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 425,189	$ 326,177
Less accumulated depreciation, depletion and amortization	143,318	161,630
Property, plant and equipment, net	281,871	164,547
Machinery, equipment and automotive [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	253,317	239,322
Machinery, equipment and automotive [Member] | Minimum [Member]
Property, Plant and Equipment [Line Items]
Useful lives in years	3 years
Machinery, equipment and automotive [Member] | Maximum [Member]
Property, Plant and Equipment [Line Items]
Useful lives in years	30 years
Buildings and improvements [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	44,248	39,381
Buildings and improvements [Member] | Minimum [Member]
Property, Plant and Equipment [Line Items]
Useful lives in years	8 years
Buildings and improvements [Member] | Maximum [Member]
Property, Plant and Equipment [Line Items]
Useful lives in years	30 years
Furniture, fixtures and store equipment [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	6,718	5,926
Furniture, fixtures and store equipment [Member] | Minimum [Member]
Property, Plant and Equipment [Line Items]
Useful lives in years	3 years
Furniture, fixtures and store equipment [Member] | Maximum [Member]
Property, Plant and Equipment [Line Items]
Useful lives in years	10 years
Assets under capital leases [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	1,468	2,105
Useful lives in years	10 years
Land improvements [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	1,148	1,080
Useful lives in years	10 years
Proved natural gas properties [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	49,801
Construction in progress [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	52,673	23,714
Capital spare parts [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	5,430	7,407
Land [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 10,386	$ 7,242