SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Revenue and Receivable Concentrations - (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 30, 2016	Jan. 01, 2016	Dec. 31, 2014
Concentrations
Concentrations amount, gross	$ 120,514	$ 109,784
Allowances	(21,302)	(17,514)
Accounts Receivable, Net, Current, Total	$ 99,212	$ 92,270
Revenue | Revenue concentration
Concentrations
Concentrations (as a percent)	100.00%	100.00%	100.00%
Revenue | Revenue concentration | Wisconsin
Concentrations
Concentrations (as a percent)	0.90%	0.00%
Revenue | Revenue concentration | Medicare program
Concentrations
Concentrations (as a percent)	68.20%	71.40%	72.40%
Revenue | Revenue concentration | Medicaid and other government programs
Concentrations
Concentrations (as a percent)	23.20%	22.50%	19.60%
Revenue | Revenue concentration | Medicaid and other government programs | Ohio
Concentrations
Concentrations (as a percent)	9.60%	9.10%	8.80%
Revenue | Revenue concentration | Medicaid and other government programs | Connecticut
Concentrations
Concentrations (as a percent)	5.00%	5.50%	5.50%
Revenue | Revenue concentration | Medicaid and other government programs | Kentucky
Concentrations
Concentrations (as a percent)	2.30%	3.20%	2.50%
Revenue | Revenue concentration | Medicaid and other government programs | New York
Concentrations
Concentrations (as a percent)	1.00%	1.70%	1.80%
Revenue | Revenue concentration | Medicaid and other government programs | Tennessee
Concentrations
Concentrations (as a percent)	4.00%	1.70%
Revenue | Revenue concentration | Medicaid and other government programs | Florida
Concentrations
Concentrations (as a percent)	0.30%	0.90%	0.60%
Revenue | Revenue concentration | Medicaid and other government programs | Others
Concentrations
Concentrations (as a percent)	0.10%	0.40%	0.40%
Revenue | Revenue concentration | All other payors
Concentrations
Concentrations (as a percent)	8.60%	6.10%	8.00%
Accounts receivable | Receivable concentration
Concentrations
Concentrations (as a percent)	100.00%	100.00%
Accounts receivable | Receivable concentration | Medicare program
Concentrations
Concentrations (as a percent)	53.20%	45.90%
Concentrations amount, gross	$ 64,128	$ 50,369
Accounts receivable | Receivable concentration | Medicaid and other government programs
Concentrations
Concentrations (as a percent)	32.20%	26.90%
Concentrations amount, gross	$ 38,825	$ 29,478
Accounts receivable | Receivable concentration | Medicaid and other government programs | Ohio
Concentrations
Concentrations (as a percent)	9.10%	7.90%
Concentrations amount, gross	$ 10,937	$ 8,627
Accounts receivable | Receivable concentration | Medicaid and other government programs | Connecticut
Concentrations
Concentrations (as a percent)	5.60%	2.50%
Concentrations amount, gross	$ 6,735	$ 2,693
Accounts receivable | Receivable concentration | Medicaid and other government programs | Kentucky
Concentrations
Concentrations (as a percent)	3.10%	2.80%
Concentrations amount, gross	$ 3,741	$ 3,055
Accounts receivable | Receivable concentration | Medicaid and other government programs | Wisconsin
Concentrations
Concentrations (as a percent)	3.70%
Concentrations amount, gross	$ 4,451
Accounts receivable | Receivable concentration | Medicaid and other government programs | New York
Concentrations
Concentrations (as a percent)	2.70%	2.90%
Concentrations amount, gross	$ 3,216	$ 3,207
Accounts receivable | Receivable concentration | Medicaid and other government programs | Tennessee
Concentrations
Concentrations (as a percent)	4.80%	7.30%
Concentrations amount, gross	$ 5,756	$ 8,038
Accounts receivable | Receivable concentration | Medicaid and other government programs | Florida
Concentrations
Concentrations (as a percent)	2.80%	2.50%
Concentrations amount, gross	$ 3,338	$ 2,702
Accounts receivable | Receivable concentration | Medicaid and other government programs | Others
Concentrations
Concentrations (as a percent)	0.50%	1.10%
Concentrations amount, gross	$ 651	$ 1,156
Accounts receivable | Receivable concentration | All other payors
Concentrations
Concentrations (as a percent)	14.60%	27.30%
Concentrations amount, gross	$ 17,561	$ 29,937
Accounts receivable net of contractual allowances
Concentrations
Concentrations (as a percent)	100.00%	100.00%
Accounts receivable net of contractual allowances | Medicare program
Concentrations
Concentrations (as a percent)	53.00%	46.00%
Accounts receivable net of contractual allowances | Medicaid and other government programs
Concentrations
Concentrations (as a percent)	32.00%	27.00%
Accounts receivable net of contractual allowances | Self Pay
Concentrations
Concentrations (as a percent)	2.00%	9.00%
Accounts receivable net of contractual allowances | Insurance
Concentrations
Concentrations (as a percent)	13.00%	18.00%
0-90 | Accounts receivable net of contractual allowances
Concentrations
Concentrations (as a percent)	48.00%	51.00%
0-90 | Accounts receivable net of contractual allowances | Medicare program
Concentrations
Concentrations (as a percent)	27.00%	26.00%
0-90 | Accounts receivable net of contractual allowances | Medicaid and other government programs
Concentrations
Concentrations (as a percent)	15.00%	12.00%
0-90 | Accounts receivable net of contractual allowances | Self Pay
Concentrations
Concentrations (as a percent)	1.00%	6.00%
0-90 | Accounts receivable net of contractual allowances | Insurance
Concentrations
Concentrations (as a percent)	6.00%	7.00%
91-180 | Accounts receivable net of contractual allowances
Concentrations
Concentrations (as a percent)	21.00%	17.00%
91-180 | Accounts receivable net of contractual allowances | Medicare program
Concentrations
Concentrations (as a percent)	13.00%	10.00%
91-180 | Accounts receivable net of contractual allowances | Medicaid and other government programs
Concentrations
Concentrations (as a percent)	5.00%	4.00%
91-180 | Accounts receivable net of contractual allowances | Self Pay
Concentrations
Concentrations (as a percent)	0.00%	1.00%
91-180 | Accounts receivable net of contractual allowances | Insurance
Concentrations
Concentrations (as a percent)	2.00%	2.00%
181-365 | Accounts receivable net of contractual allowances
Concentrations
Concentrations (as a percent)	14.00%	21.00%
181-365 | Accounts receivable net of contractual allowances | Medicare program
Concentrations
Concentrations (as a percent)	8.00%	7.00%
181-365 | Accounts receivable net of contractual allowances | Medicaid and other government programs
Concentrations
Concentrations (as a percent)	4.00%	8.00%
181-365 | Accounts receivable net of contractual allowances | Self Pay
Concentrations
Concentrations (as a percent)	0.00%	1.00%
181-365 | Accounts receivable net of contractual allowances | Insurance
Concentrations
Concentrations (as a percent)	2.00%	5.00%
>1 yr. | Accounts receivable net of contractual allowances
Concentrations
Concentrations (as a percent)	17.00%	11.00%
>1 yr. | Accounts receivable net of contractual allowances | Medicare program
Concentrations
Concentrations (as a percent)	5.00%	3.00%
>1 yr. | Accounts receivable net of contractual allowances | Medicaid and other government programs
Concentrations
Concentrations (as a percent)	8.00%	3.00%
>1 yr. | Accounts receivable net of contractual allowances | Self Pay
Concentrations
Concentrations (as a percent)	0.00%	1.00%
>1 yr. | Accounts receivable net of contractual allowances | Insurance
Concentrations
Concentrations (as a percent)	4.00%	4.00%