Fair Value (Details Textual) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Fair Value (Additional Textual) [Abstract]
Mark-to-market adjustment	$ 7	$ (10)
Total losses related to derivative instrument	410	1,129	844
Future [Member]
Fair Value (Textual) [Abstract]
Notional amounts of futures contracts outstanding	2,000	3,500
Average notional amounts of futures contracts outstanding	$ 4,700	$ 5,400