DEBT - Athyrium Credit Facility (Details) $ / shares in Units, $ in Thousands		3 Months Ended		6 Months Ended		12 Months Ended
	Oct. 01, 2018 USD ($) $ / shares shares	Jun. 30, 2020 USD ($) item $ / shares	Jun. 30, 2019 USD ($)	Jun. 30, 2020 USD ($) item $ / shares shares	Jun. 30, 2019 USD ($)	Dec. 31, 2019 USD ($) shares	Dec. 31, 2018 USD ($)
Debt instruments
Warrant exercisable | shares				248,505		297,988
Effective interest rate		11.63%	11.63%	11.63%	11.63%
Interest expense		$ 2,134	$ 2,061	$ 4,262	$ 4,155
Warrants 2018
Debt instruments
Exercise Price | $ / shares		$ 12.18		$ 12.18
Warrant exercisable | shares				184,660		184,660
Remaining warrant exercisable upon condition | shares				86,175		86,175
Athyrium Credit Facility
Debt instruments
Aggregate principal amount	$ 110,000	$ 75,000		$ 75,000			$ 75,000
Cumulative accretion of exit fee		$ 256		$ 256			183
Present value of prepayments if prepayment occurs prior to the second anniversary (as a percent)	105.00%
Prepayments if prepayment occurs on or after the second anniversary of the applicable date of issuance but prior to the third anniversary (as a percent)	3.00%
Prepayments if prepayment occurs on or after the third anniversary (as a percent)	2.00%
Prepayments if prepayment occurs after the fourth anniversary (as a percent)	0.00%
Additional interest rate upon an event of default accrued (as a percent)	3.00%
Total interest rate (as a percent)	12.875%
Number of features of embedded derivative | item				2
Number of derivatives | item		1		1
Financial covenant amount	$ 10,000
Restricted Cash and Cash Equivalents		$ 10,000		$ 10,000		$ 10,000
Debt issuance costs		3,559		3,559			$ 3,999
Interest expense		2,100	2,100	4,200	4,100
Amortization of debt discount		200	200	400	400
Contractual coupon interest		$ 1,900	$ 1,900	$ 3,800	$ 3,700
Athyrium Credit Facility | Warrants 2018
Debt instruments
Warrant to purchase shares of common stock | shares	270,835
Exercise Price | $ / shares	$ 12.18456
Warrant exercisable | shares	184,660
Remaining warrant exercisable upon condition | shares	86,175
Initial fair value of the Warrant	$ 1,900
Term Loan A
Debt instruments
Aggregate principal amount	$ 75,000
Interest rate (as a percent)	9.875%
Exit fee of the total principal payments (as a percent)	1.00%
Cumulative accretion of exit fee	$ 700
Term Loan B
Debt instruments
Aggregate principal amount	$ 35,000