REVENUE RECOGNITION - Narrative (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenues	$ 165,649,000	$ 154,016,000	$ 313,104,000	$ 287,818,000
Revenue recognized	0		0
Gross receivables from contracts	77,822,000		77,822,000		$ 66,227,000
Contract liabilities	2,115,000		2,115,000		$ 1,823,000
Adjustments | Accounting Standards Update 2014-09
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenues	$ 1,616		$ 3,084