Property and Equipment, net (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 66,919	$ 69,835
Less: Accumulated depreciation	57,103	60,284
Property, plant and equipment, excluding construction in progress, net	9,816	9,551
Construction in progress	329	652
Total	10,145	10,203
Depreciation expense	$ 2,800	2,200	$ 2,500
Minimum
Property, Plant and Equipment [Line Items]
Estimated Useful Life (in years)	3 years
Maximum
Property, Plant and Equipment [Line Items]
Estimated Useful Life (in years)	30 years
Railroad and equipment
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 33,626	33,627
Railroad and equipment | Minimum
Property, Plant and Equipment [Line Items]
Estimated Useful Life (in years)	15 years
Railroad and equipment | Maximum
Property, Plant and Equipment [Line Items]
Estimated Useful Life (in years)	30 years
Machinery and equipment
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 15,587	16,498
Machinery and equipment | Minimum
Property, Plant and Equipment [Line Items]
Estimated Useful Life (in years)	3 years
Machinery and equipment | Maximum
Property, Plant and Equipment [Line Items]
Estimated Useful Life (in years)	10 years
Office equipment
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 16,662	18,844
Office equipment | Minimum
Property, Plant and Equipment [Line Items]
Estimated Useful Life (in years)	3 years
Office equipment | Maximum
Property, Plant and Equipment [Line Items]
Estimated Useful Life (in years)	10 years
Autos and trucks
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 1,044	$ 866
Autos and trucks | Minimum
Property, Plant and Equipment [Line Items]
Estimated Useful Life (in years)	3 years
Autos and trucks | Maximum
Property, Plant and Equipment [Line Items]
Estimated Useful Life (in years)	10 years