SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Net Service Revenues - (Details) - Medicare program $ in Thousands	12 Months Ended
	Dec. 29, 2017 USD ($) item	Dec. 30, 2016 USD ($)	Jan. 01, 2016 USD ($)
Net service revenues
Segment Reporting Sales Revenue Services Net Percentage	75.00%
Period of episode payment rate	60 days
Outlier payments (as a percent)	10.00%
Percentage of reduction for sequestration	2
Increase (decrease) in revenues due to changes in estimates related to prior periods | $	$ (780)	$ (608)	$ (365)
Minimum
Net service revenues
Number of therapy service visits, level one threshold	6
Number of therapy service visits, level two threshold	14
Number of therapy service visits, level three threshold	20
Maximum
Net service revenues
Number of visits for avoiding low utilization payment adjustment	5