Contingencies Remediation Liability (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Loss Contingencies [Line Items]
Accrued Environmental Loss Contingencies, Current	$ 17,922	$ 18,176	$ 20,603
Accrual for Environmental Loss Contingencies, Charges to Expense for New Losses	97	556
Accrual for Environmental Loss Contingencies, Payments	$ (351)	$ (2,983)