FAIR VALUE MEASUREMENTS - Narrative (Details) $ in Millions	6 Months Ended
	Jun. 30, 2017 USD ($)
Level 3 | Obligations
Financial instruments
Volatility of future revenue (as a percent)	50.00%
Level 3 | Obligations | Minimum
Financial instruments
Discount rate	1.00%
Probability of milestone achievement (as a percent)	43.00%
Level 3 | Obligations | Maximum
Financial instruments
Discount rate	3.00%
Probability of milestone achievement (as a percent)	85.00%
Fair value | Level 2
Financial instruments
Fair value of notes payable	$ 607.2
Carrying value | Level 2
Financial instruments
Fair value of notes payable	$ 598.4