SUBSEQUENT EVENTS (Details) - USD ($)	Apr. 18, 2019	Apr. 01, 2019	Aug. 22, 2017	Mar. 31, 2019	Dec. 31, 2018	Jul. 01, 2016
Subsequent Event [Line Items]
Total credit facilities outstanding				$ 0
Maximum borrowing capacity				117,500,000		$ 117,500,000
Kern Radiology Imaging Systems, Inc. | Subsequent Event
Subsequent Event [Line Items]
Purchase consideration		$ 19,300,000
Zilkha Radiology | Subsequent Event
Subsequent Event [Line Items]
Purchase consideration		$ 4,500,000
Revolving Credit Facility
Subsequent Event [Line Items]
Total credit facilities outstanding				41,000,000	$ 28,000,000
Maximum borrowing capacity				$ 69,600,000
Line of Credit | Revolving Credit Facility | First Lien Credit Agreement, Fifth Amendment
Subsequent Event [Line Items]
Periodic payment, principal			$ 8,300,000
Line of Credit | Revolving Credit Facility | First Lien Credit Agreement, Sixth Amendment | Subsequent Event
Subsequent Event [Line Items]
Additional revolving commitments	$ 20,000,000
Maximum borrowing capacity	$ 137,500,000
Line of Credit | Revolving Credit Facility | First Lien Credit Agreement, Seventh Amendment | Subsequent Event
Subsequent Event [Line Items]
Term increase	2 years
Periodic payment, principal	$ 9,700,000
Medium-term Notes | First Lien Credit Agreement, Fifth Amendment
Subsequent Event [Line Items]
Total credit facilities outstanding			$ 100,000,000
Medium-term Notes | First Lien Credit Agreement, Sixth Amendment | Subsequent Event
Subsequent Event [Line Items]
Total credit facilities outstanding	$ 679,000,000