Edith River Derailment (Details)	3 Months Ended			3 Months Ended							12 Months Ended
	Mar. 31, 2013 USD ($)	Mar. 31, 2012 USD ($)	Dec. 31, 2012 USD ($)	Mar. 31, 2013 Edith River Derailment [Member] USD ($)	Mar. 31, 2013 Edith River Derailment [Member] AUD	Jun. 30, 2012 Edith River Derailment [Member] USD ($)	Jun. 30, 2012 Edith River Derailment [Member] AUD	Mar. 31, 2012 Edith River Derailment [Member] USD ($)	Dec. 31, 2011 Edith River Derailment [Member] USD ($)	Dec. 31, 2011 Edith River Derailment [Member] AUD	Dec. 31, 2012 Edith River Derailment [Member] USD ($)	Dec. 31, 2012 Edith River Derailment [Member] AUD	Mar. 31, 2013 Accounts receivable insurance claims [Member] USD ($)	Dec. 31, 2012 Accounts receivable insurance claims [Member] USD ($)	Dec. 31, 2011 Accounts receivable insurance claims [Member] Edith River Derailment [Member] USD ($)	Dec. 31, 2011 Accounts receivable insurance claims [Member] Edith River Derailment [Member] AUD
Lost revenues								$ 7,000,000
Lost income from operations due to a specified event								5,000,000
Gain on business interruption insurance recovery						4,800,000	4,800,000
Estimated accrued repair costs									15,300,000	15,000,000	13,300,000	12,800,000
Accounts receivable	266,217,000		265,642,000										15,158,000	26,443,000	14,300,000	14,000,000
Accounts receivable insurance claims						4,800,000	4,804,000
Insurance deductible									1,021,000	1,000,000
Payment of derailment costs				900,000	900,000						27,300,000	26,300,000
Insurance proceeds received	$ 9,315,000	$ 12,521,000		$ 9,300,000	9,000,000						$ 20,900,000	22,100,000