Unconsolidated Subsidiaries (Details) (USD $)	3 Months Ended		9 Months Ended											3 Months Ended		9 Months Ended		3 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014 Subsidiaries	Sep. 30, 2013	Dec. 31, 2013	Sep. 30, 2014 Coyote Creek	Dec. 31, 2013 Coyote Creek	Sep. 30, 2013 Coyote Creek	Sep. 30, 2014 Other noncurrent assets	Dec. 31, 2013 Other noncurrent assets	Sep. 30, 2013 Other noncurrent assets	Sep. 30, 2014 Liberty T	Sep. 30, 2014 Coyote Creek T	Sep. 30, 2014 Variable interest entity, not primary beneficiary	Sep. 30, 2013 Variable interest entity, not primary beneficiary	Sep. 30, 2014 Variable interest entity, not primary beneficiary	Sep. 30, 2013 Variable interest entity, not primary beneficiary	Jun. 30, 2014 NACC India customer Allowance for doubtful accounts	Sep. 30, 2014 Minimum Camino Real T	Sep. 30, 2014 Maximum Camino Real T
Variable Interest Entity [Line Items]
Number of wholly owned subsidiaries			2
Production capacity												4,300,000	2,500,000						2,500,000	3,000,000
Valuation allowances and reserves, adjustments																		$ 1,100,000
Investment in unconsolidated operations and related tax position									28,900,000	33,100,000	35,200,000
Variable interest entity, reporting entity involvement, maximum risk of loss	3,800,000	5,000,000	3,800,000	5,000,000	5,400,000
Accounts receivable from affiliates	44,339,000	30,551,000	44,339,000	30,551,000	32,636,000	42,200,000	27,900,000	26,700,000
Revenues	221,714,000	228,614,000	599,497,000	620,683,000										150,529,000	152,999,000	437,127,000	433,937,000
Gross profit	46,543,000	49,219,000	119,237,000	143,110,000										19,504,000	18,847,000	56,123,000	55,859,000
Income before income taxes														12,201,000	12,172,000	36,363,000	35,650,000
Net income	$ 7,699,000	$ 12,325,000	$ 2,551,000	$ 21,894,000										$ 9,372,000	$ 9,471,000	$ 28,046,000	$ 27,463,000