SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Property and Equipment (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Property and Equipment
Impairment charges related to property and equipment	$ 0	$ 0	$ 0
Computer hardware and software | Minimum
Property and Equipment
Useful Life	3 years
Computer hardware and software | Maximum
Property and Equipment
Useful Life	5 years
Office equipment
Property and Equipment
Useful Life	5 years
Vehicles | Minimum
Property and Equipment
Useful Life	4 years
Vehicles | Maximum
Property and Equipment
Useful Life	5 years
Medical equipment | Minimum
Property and Equipment
Useful Life	13 months
Medical equipment | Maximum
Property and Equipment
Useful Life	5 years
Furniture and fixtures
Property and Equipment
Useful Life	5 years