Commitments and Contingencies (Details) (USD $)	1 Months Ended	6 Months Ended
	Jul. 31, 2012	Jun. 30, 2012 vessel
Notes payable to bank
Contingencies
Letters of credit outstanding related to supply agreements		$ 30,469,000
Letters of credit for outstanding Industrial Development Revenue Bonds		26,385,000
Letters of credit related to insurance coverages		21,765,000
Committed bank line
Contingencies
Letters of credit outstanding		78,850,000
Uncommitted bank lines
Contingencies
Letters of credit outstanding		8,690,000
Commodity Trading and Milling
Contingencies
Number of dry bulk vessels to be built		4
Cost of dry bulk vessels to be built		83,000,000
Amount paid under the down payment	8,300,000
Debt guarantees of non-consolidated affiliates and third party
Contingencies
Number of third parties to whom guarantees are outstanding		3
Maximum exposure for guarantees outstanding		$ 1,131,000