ORGANIZATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Segment (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2018 USD ($) item	Mar. 31, 2017 USD ($)
Summary of Significant Accounting Policies
Labor warranty	90 days
Manufacturer warranty	180 days
Number of performance obligations | item	2
Maximum cranial device follow up visit period	90 days
Net revenue	$ 233,995
Patient Care
Summary of Significant Accounting Policies
Net revenue	188,507
Patient Care | Before adoption of ASC 606
Summary of Significant Accounting Policies
Net revenue		$ 187,637
Patient Care | Medicare
Summary of Significant Accounting Policies
Net revenue	57,531
Patient Care | Medicare | Before adoption of ASC 606
Summary of Significant Accounting Policies
Net revenue		55,245
Patient Care | Medicaid
Summary of Significant Accounting Policies
Net revenue	29,711
Patient Care | Medicaid | Before adoption of ASC 606
Summary of Significant Accounting Policies
Net revenue		28,292
Patient Care | Commercial insurance (excluding Medicare and Medicaid Managed Care)
Summary of Significant Accounting Policies
Net revenue	70,582
Patient Care | Commercial insurance (excluding Medicare and Medicaid Managed Care) | Before adoption of ASC 606
Summary of Significant Accounting Policies
Net revenue		74,166
Patient Care | Veterans Administration
Summary of Significant Accounting Policies
Net revenue	16,731
Patient Care | Veterans Administration | Before adoption of ASC 606
Summary of Significant Accounting Policies
Net revenue		15,572
Patient Care | Private pay
Summary of Significant Accounting Policies
Net revenue	13,952
Patient Care | Private pay | Before adoption of ASC 606
Summary of Significant Accounting Policies
Net revenue		14,362
Products & Services
Summary of Significant Accounting Policies
Net revenue	$ 45,488
Products & Services | Minimum
Summary of Significant Accounting Policies
Payment terms	30 days
Products & Services | Maximum
Summary of Significant Accounting Policies
Payment terms	90 days
Products & Services | Before adoption of ASC 606
Summary of Significant Accounting Policies
Net revenue		46,044
Products & Services | Distribution, net of intersegment revenue eliminations
Summary of Significant Accounting Policies
Net revenue	$ 31,351
Products & Services | Distribution, net of intersegment revenue eliminations | Before adoption of ASC 606
Summary of Significant Accounting Policies
Net revenue		30,624
Products & Services | Therapeutic solutions
Summary of Significant Accounting Policies
Net revenue	$ 14,137
Products & Services | Therapeutic solutions | Before adoption of ASC 606
Summary of Significant Accounting Policies
Net revenue		$ 15,420