ACCRUED AND OTHER LIABILITIES - Environmental Reserves (Details) $ in Thousands		3 Months Ended			6 Months Ended	12 Months Ended		24 Months Ended
	Sep. 30, 2016 USD ($)	Mar. 31, 2019 USD ($)	Dec. 31, 2017 USD ($)	Jun. 30, 2016 USD ($)	Jun. 30, 2019 USD ($)	Dec. 31, 2015 USD ($) a	Dec. 31, 2014 USD ($) a	Dec. 31, 2015 USD ($) a	Mar. 31, 2017 USD ($)
Environmental Reserve for Monitoring Environmental Remediation Work Previously Performed
Environmental reserves
Additional environmental reserve accrued			$ 51			$ 500	$ 110	$ 661
Environmental costs funded					$ 577
Environmental reserve accrued					84
Wetlands restoration
Environmental reserves
Acres of land | a						148.4		148.4
Estimated cost	$ 2,000	$ 2,400		$ 2,000	2,400
Environmental costs funded					2,200
Accrued restoration cost					$ 208	$ 1,700		$ 1,700	$ 713
Increase in accrual of remediation costs		$ 361		$ 300
Minimum | Environmental Reserve for Monitoring Environmental Remediation Work Previously Performed
Environmental reserves
Estimated cost						500
Minimum | Wetlands restoration
Environmental reserves
Estimated cost						1,700
Maximum | Environmental Reserve for Monitoring Environmental Remediation Work Previously Performed
Environmental reserves
Acres of land | a							1
Estimated cost						1,000
Maximum | Wetlands restoration
Environmental reserves
Estimated cost						$ 1,900