Fair Value (Tables)

3 Months Ended

Mar. 31, 2015

Fair Value Disclosures [Abstract]

Fair Value Measurements, Recurring and Nonrecurring [Table Text Block]

	Fair Value at										Fair Value at
Asset / (Liability) (dollars in thousands)	March 31, 2015										December 31, 2014
	Level 1		Level 2			Level 3		Total			Level 1		Level 2			Level 3		Total
Commodity futures natural gas contracts	$	—	$	(3,489	)	$	—	$	(3,489	)	$	—	$	(2,868	)	$	—	$	(2,868	)
Currency contracts	—		477			—		477			—		403			—		403
Net derivative asset (liability)	$	—	$	(3,012	)	$	—	$	(3,012	)	$	—	$	(2,465	)	$	—	$	(2,465	)

Fair Value, by Balance Sheet Grouping [Table Text Block]

The total derivative position is recorded on the Condensed Consolidated Balance Sheets as follows:

Asset / (Liability) (dollars in thousands)	March 31, 2015			December 31, 2014
Prepaid and other current assets	$	477		$	403
Derivative liability	(3,151		)	(2,653		)
Other long-term liabilities	(338		)	(215		)
Net derivative asset (liability)	$	(3,012	)	$	(2,465	)