OTHER BALANCE SHEET INFORMATION - Other Noncurrent Liabilities (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Other non-current liabilities:
Asset retirement obligations	$ 9,099	$ 9,018
Environmental liabilities	2,301	2,227
Accrued sales, use and other taxes	17,005	17,024
Operating leases	3,803	0
Other	79	67
Total	$ 32,287	$ 28,336

Carrying value of the obligation (known or estimated) arising from requirements to perform activities to remediate one or more sites, payable after twelve months or beyond the next operating cycle if longer.

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