Derivative Instruments (Effect of Derivative Instruments on Operations) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Derivative [Line Items]
Income / (Expense)	$ 3,937	$ 3,395	$ 2,582
Total derivatives designated as hedging instruments
Derivative [Line Items]
Income / (Expense)	2,655	2,620	0
Total derivatives designated as hedging instruments | Cost of goods sold | Commodity contracts
Derivative [Line Items]
Income / (Expense)	2,655	2,620	0
Total derivatives not designated as hedging instruments
Derivative [Line Items]
Income / (Expense)	1,282	775	2,582
Total derivatives not designated as hedging instruments | Cost of goods sold | Commodity contracts
Derivative [Line Items]
Income / (Expense)	131	(92)	0
Total derivatives not designated as hedging instruments | Realized and unrealized gain on derivatives | Commodity contracts
Derivative [Line Items]
Income / (Expense)	1,307	1,988	522
Total derivatives not designated as hedging instruments | Realized and unrealized gain on derivatives | Derivative features of Subordinated Notes
Derivative [Line Items]
Income / (Expense)	0	(793)	2,060
Total derivatives not designated as hedging instruments | Interest expense | Interest rate swap agreements
Derivative [Line Items]
Income / (Expense)	$ (156)	$ (328)	$ 0