SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Fair Value of Assets and Liabilities Measured on a Recurring Basis (Details) - USD ($)	Sep. 30, 2019	Mar. 31, 2019	Dec. 31, 2018
Assets:
U.S. treasuries	$ 18,500,000		$ 0
Liabilities:
Warrant liability	0	$ 1,500,000	242,000
Fair Value, Recurring | Level 1
Assets:
Money market funds	7,225,000		8,067,000
U.S. treasuries	18,473,000
Total	25,698,000
Liabilities:
Contingent consideration	0		0
Warrant liability			0
Total			0
Fair Value, Recurring | Level 2
Assets:
Money market funds	0		0
U.S. treasuries	0
Total	0
Liabilities:
Contingent consideration	0		0
Warrant liability			0
Total			0
Fair Value, Recurring | Level 3
Assets:
Money market funds	0		0
U.S. treasuries	0
Total	0
Liabilities:
Contingent consideration	$ 145,000		145,000
Warrant liability			242,000
Total			$ 387,000