ACCRUED AND OTHER LIABILITIES - Environmental Reserves (Details) $ in Thousands		3 Months Ended			12 Months Ended		24 Months Ended
	Sep. 30, 2016 USD ($)	Mar. 31, 2019 USD ($)	Dec. 31, 2017 USD ($)	Jun. 30, 2016 USD ($)	Dec. 31, 2015 USD ($) a	Dec. 31, 2014 USD ($) a	Dec. 31, 2015 USD ($) a
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 | a					148.4		148.4
Estimated cost	$ 2,000	2,400		$ 2,000
Environmental costs funded		1,700
Accrued restoration cost		713			$ 1,700		$ 1,700
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 | a						1
Estimated cost					1,000
Maximum | Wetlands restoration
Environmental reserves
Estimated cost					$ 1,900