Fair value measurements (Details) (USD $)		3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2012 Derivative Liabilities - Net [Member]	Sep. 30, 2011 Derivative Liabilities - Net [Member]	Sep. 30, 2012 Derivative Liabilities - Net [Member]	Sep. 30, 2011 Derivative Liabilities - Net [Member]	Sep. 30, 2012 Fair Value, Measurements, Recurring [Member]	Dec. 31, 2011 Fair Value, Measurements, Recurring [Member]	Sep. 30, 2012 Fair Value, Measurements, Recurring [Member] Fair Value, Inputs, Level 1 [Member]	Dec. 31, 2011 Fair Value, Measurements, Recurring [Member] Fair Value, Inputs, Level 1 [Member]	Sep. 30, 2012 Fair Value, Measurements, Recurring [Member] Fair Value, Inputs, Level 2 [Member]	Dec. 31, 2011 Fair Value, Measurements, Recurring [Member] Fair Value, Inputs, Level 2 [Member]	Sep. 30, 2012 Fair Value, Measurements, Recurring [Member] Fair Value, Inputs, Level 3 [Member]	Dec. 31, 2011 Fair Value, Measurements, Recurring [Member] Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Embedded Derivative, Fair Value of Embedded Derivative, Net	$ 0
ASSETS:
Cash equivalents						167,325,000	176,284,000	167,325,000	176,284,000	0	0	0	0
Trust assets						14,572,000	15,889,000	14,572,000	15,889,000	0	0	0	0
Surety bond – workers comp insurance						2,381,000	2,391,000	2,381,000	2,391,000	0	0	0	0
Primary aluminum put option contracts							9,331,000		0		9,331,000		0
Power contract							106,000		0		0		106,000
TOTAL						184,278,000	204,001,000	184,278,000	194,564,000	0	9,331,000	0	106,000
LIABILITIES:
Natural gas forward financial contracts							281,000		0		281,000		0
E.ON contingent obligation – net						15,016,000	13,958,000	0	0	0	0	15,016,000	13,958,000
Primary aluminum sales contract – premium collar						1,379,000	908,000	0	0	0	0	1,379,000	908,000
TOTAL						16,395,000	15,147,000	0	0	0	281,000	16,395,000	14,866,000
Level 3 fair value measurements [Roll Forward]
Beginning balance		(16,024,000)	(14,536,000)	(14,760,000)	(13,802,000)
Total gain (realized/unrealized) included in earnings		(371,000)	(45,000)	(1,529,000)	(1,275,000)
Settlements		0	(29,000)	(106,000)	467,000
Ending balance		(16,395,000)	(14,610,000)	(16,395,000)	(14,610,000)
Amount of total loss included in earnings attributable to the change in unrealized losses (gains) relating to assets and liabilities held		$ (371,000)	$ (45,000)	$ (1,529,000)	$ (1,275,000)