MARKETABLE SECURITIES AND FAIR VALUE - Fair Value Hierarchy (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Assets:
Estimated Fair Value	$ 3,192
Corporate obligations
Assets:
Estimated Fair Value	3,192
Fair Value, Recurring
Assets:
Cash and cash equivalents	111,565	$ 91,803
Total	114,757	91,803
Fair Value, Recurring | Level 1
Assets:
Cash and cash equivalents	111,565	91,803
Total	111,565	91,803
Fair Value, Recurring | Level 2
Assets:
Cash and cash equivalents	0	0
Total	3,192	0
Fair Value, Recurring | Level 3
Assets:
Cash and cash equivalents	0	0
Total	0	$ 0
Fair Value, Recurring | Corporate obligations
Assets:
Estimated Fair Value	3,192
Fair Value, Recurring | Corporate obligations | Level 1
Assets:
Estimated Fair Value	0
Fair Value, Recurring | Corporate obligations | Level 2
Assets:
Estimated Fair Value	3,192
Fair Value, Recurring | Corporate obligations | Level 3
Assets:
Estimated Fair Value	$ 0