GOODWILL AND INTANGIBLE ASSETS - Summary of Amortizable Intangible Asset (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018
Finite-Lived Intangible Assets [Line Items]
Intangible assets gross	$ 31,685	$ 31,685
Accumulated amortization	(6,298)	(5,514)
Intangible assets, Net	25,387	26,171
Goodwill, Gross	63,945	63,945
Goodwill	63,945	63,945	$ 63,945	$ 63,945	$ 63,945
Intangible Assets, Net (Including Goodwill) [Abstract]
Total intangible assets & goodwill, Gross	95,630	95,630
Total intangible assets & goodwill, Net	89,332	90,116
Non-compete agreements
Finite-Lived Intangible Assets [Line Items]
Intangible assets gross	2	2
Accumulated amortization	(2)	(2)
Intangible assets, Net	$ 0	$ 0
Useful life	2 years	2 years
Brand and tradenames
Finite-Lived Intangible Assets [Line Items]
Intangible assets gross	$ 1,695	$ 1,695
Accumulated amortization	(527)	(470)
Intangible assets, Net	$ 1,168	$ 1,225
Brand and tradenames | Minimum
Finite-Lived Intangible Assets [Line Items]
Useful life	3 years	3 years
Brand and tradenames | Maximum
Finite-Lived Intangible Assets [Line Items]
Useful life	7 years	7 years
Developed technology
Finite-Lived Intangible Assets [Line Items]
Intangible assets gross	$ 10,939	$ 10,939
Accumulated amortization	(3,727)	(3,266)
Intangible assets, Net	$ 7,212	$ 7,673
Developed technology | Minimum
Finite-Lived Intangible Assets [Line Items]
Useful life	5 years	5 years
Developed technology | Maximum
Finite-Lived Intangible Assets [Line Items]
Useful life	6 years	6 years
Customer relationships
Finite-Lived Intangible Assets [Line Items]
Intangible assets gross	$ 19,049	$ 19,049
Accumulated amortization	(2,042)	(1,776)
Intangible assets, Net	$ 17,007	$ 17,273
Customer relationships | Minimum
Finite-Lived Intangible Assets [Line Items]
Useful life	10 years	10 years
Customer relationships | Maximum
Finite-Lived Intangible Assets [Line Items]
Useful life	18 years	18 years