Components of Working Capital - Accrued Liabilities Table (Details) - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015
Accrued Liabilities [Line Items]
Accrued interest expense	$ 26,204	$ 26,194
Short-term asset retirement obligations	2,713	3,677
Short-term remediation and reclamation obligations	1,136	1,136
Income taxes payable	1,127	770
Total accrued liabilities	130,159	119,096	[1]
Accrued Capital Expenditures [Member]
Accrued Liabilities [Line Items]
Other accrued liabilities	70,725	61,454
Accrued Plant Purchases [Member]
Accrued Liabilities [Line Items]
Other accrued liabilities	27,149	16,425
Other Accrued Liabilities [Member]
Accrued Liabilities [Line Items]
Other accrued liabilities	$ 1,105	$ 9,440

[1] Financial information has been recast to include the financial position and results attributable to the Springfield interest. See Note 1 and Note 2.