COMMITMENTS AND CONTINGENCIES - LEASES (Details) $ in Thousands		12 Months Ended
	Nov. 30, 2011 ft²	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)	Sep. 04, 2013 USD ($)
Commitments
Leasehold improvements, gross		$ 392
Leasehold improvements, net		185
Total rent expense		1,123	$ 1,148	$ 1,125
Amount of settlement agreement					$ 286
Cambridge Lease
Commitments
Lease Space for Laboratory and office space (in square feet) | ft²	26,150
Term of commercial lease	6 years 3 months
Term of lease extension option	5 years
Deferred rent liability		391
Standby letter of credit in favor of a landlord
Commitments
Standby letter of credit		$ 311