OPERATING SEGMENTS AND GEOGRAPHIC INFORMATION - Summary of Revenues by Country (Details) - USD ($)	3 Months Ended								12 Months Ended			50 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Sep. 30, 2018
Segment Reporting Information [Line Items]
Revenues	$ 78,238,000	$ 82,972,000	$ 81,962,000	$ 74,201,000	$ 70,035,000	$ 68,907,000	$ 69,642,000	$ 72,133,000	$ 317,373,000	$ 280,718,000	$ 298,297,000	$ 8,855
United States
Segment Reporting Information [Line Items]
Revenues									252,482,000	220,018,000	231,943,000
Canada
Segment Reporting Information [Line Items]
Revenues									38,133,000	38,750,000	44,206,000
Other countries
Segment Reporting Information [Line Items]
Revenues									$ 26,758,000	$ 21,950,000	$ 22,148,000