Inventories (Details Textual) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Inventories (Textual)
Inventories classified as long-term assets (Other noncurrent assets)	$ 19,726	$ 16,786
Inventories valued under the LIFO method	251,978	241,898
Decrease in cost of goods sold due to the effect of the LIFO liquidation	1,288	2,956	3,839
Increase in net earnings due to the effect of the LIFO liquidation	776	1,763	2,273
Excess of estimated current cost over LIFO cost	140,335	123,623
Approximate effect on net earnings due to the adoption of the LIFO method	$ 10,050	$ (3,890)	$ 2,043