Annual report pursuant to Section 13 and 15(d)

Commitments and Contingencies, Remediation Obligations (Details)

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Commitments and Contingencies, Remediation Obligations (Details) - USD ($)
$ in Thousands
Dec. 31, 2016
Dec. 31, 2015
Commitments and Contingencies Disclosure [Abstract]    
Accrual for Environmental Loss Contingencies $ 45,636 $ 46,362
Accrued Environmental Loss Contingencies, Current 4,237 7,880
Accrued Environmental Loss Contingencies, Noncurrent $ 41,399 $ 38,482
Accrual for Environmental Loss Contingencies, Discount Rate 2.62%