STOCKHOLDERS' EQUITY - Restricted Stock Unit Activity (Details) - Restricted Stock Units (RSUs) $ in Thousands	6 Months Ended
	Mar. 31, 2019 USD ($) shares
Shares
Beginning balance (in shares) | shares	2,207,242
Granted (in shares) | shares	1,713,252
Vested (in shares) | shares	(334,622)
Forfeited (in shares) | shares	(115,356)
Ending balance (in shares) | shares	3,470,516
Weighted Average Grant Date Fair Value
Beginning balance (in dollars per share) | $	$ 7,302
Granted (in dollars per share) | $	5,133
Vested (in dollars per shares) | $	(1,422)
Forfeited (in dollars per share) | $	(374)
Ending balance (in dollars per share) | $	$ 10,639