COMMITMENTS AND CONTINGENCIES - FUTURE MINIMUM LEASE PAYMENTS UNDER NON-CANCELLABLE LEASE AGREEMENTS (Details) $ in Thousands	Jun. 30, 2017 USD ($)
Operating Leases, Future Minimum Payments Due, Fiscal Year Maturity [Abstract]
2017 (remaining nine months)	$ 2,282
2018	4,296
2019	4,244
2020	4,254
2021	3,619
Thereafter	11,338
Total minimum lease payments, Operating Leases	30,033
Capital Leases, Future Minimum Payments Due, Fiscal Year Maturity [Abstract]
2017 (remaining nine months)	821
2018	1,679
2019	1,729
2020	1,781
2021	1,835
Thereafter	17,527
Total minimum lease payments, Financing Obligation Building-Leased	25,372
Contractual Obligation, Fiscal Year Maturity [Abstract]
2017 (remaining nine months)	3,103
2018	5,975
2019	5,973
2020	6,035
2021	5,454
Thereafter	28,865
Total minimum lease payments	$ 55,405