COMMITMENTS AND CONTINGENCIES, FUTURE MINIMUM RENT COMMITMENTS (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Jun. 19, 2017 USD ($)	Jun. 13, 2017 ft²	Mar. 31, 2016 USD ($) ft²
Future minimum rent commitments
2018	$ 1,380
2019	1,959
2020	2,018
2021	2,078
2022	2,141
Thereafter	1,828
Total	11,404
Commitments
Total rent expense	1,231	$ 918	$ 1,123
Sublease
Commitments
Lease space (in square feet) | ft²						5,233
Tenant security deposit and first month's rent						$ 51
Tenant security deposit						$ 26
Sublease income recorded as offset to rent expense	26	$ 230
Moderna Sublease
Commitments
Lease space (in square feet) | ft²					5,233
Tenant security deposit				$ 55
Sublease income recorded as offset to rent expense	$ 164