Contingencies - Rollforward of Remediation Reserves (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Contingencies
Accrued liabilities start of period	$ 20,603	$ 3,918	$ 5,116
Remediation expense	556	18,591	1,521
Remediation payments	(2,983)	(1,906)	(2,719)
Accrued liabilities end of period	$ 18,176	$ 20,603	$ 3,918