Accrued Liabilities - Components of Accrued Liabilities (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018	Dec. 31, 2017
Accrued Liabilities
Accrued product related costs	$ 4,036	$ 4,377
Accrued income taxes	6,315	6,914
Accrued property and other taxes	1,810	1,976
Accrued professional fees	2,474	3,350
Contract with Customer, Liability	2,263	1,981
Dividends payable	1,309	1,310
Remediation reserves	10,564	11,274	$ 17,067
Other accrued liabilities	4,625	6,165
Total accrued liabilities	$ 33,396	$ 37,347