Contingencies - Rollforward of Remediation Reserves (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Contingencies
Accrued liabilities start of period	$ 11,274	$ 17,067	$ 18,176
Remediation expense	2,602	1,182	307
Remediation payments	(2,455)	(6,967)	(1,416)
Other activity	23	(8)	0
Accrued liabilities end of period	$ 11,444	$ 11,274	$ 17,067