SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Revenue and Receivable Concentrations - (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 29, 2017	Dec. 30, 2016	Jan. 01, 2016
Concentrations
Concentrations amount, gross	$ 154,041	$ 120,514
Allowances	(28,181)
Accounts Receivable, Net, Current, Total	$ 125,860	$ 99,212
Revenue \| Revenue concentration
Concentrations
Concentrations (as a percent)	100.00%	100.00%	100.00%
Revenue \| Revenue concentration \| Wisconsin
Concentrations
Concentrations (as a percent)	1.40%	0.90%
Revenue \| Revenue concentration \| Medicare program
Concentrations
Concentrations (as a percent)	75.10%	68.20%	71.40%
Revenue \| Revenue concentration \| Medicaid and other government programs
Concentrations
Concentrations (as a percent)	19.80%	23.20%	22.50%
Revenue \| Revenue concentration \| Medicaid and other government programs \| Ohio
Concentrations
Concentrations (as a percent)	7.50%	9.60%	9.10%
Revenue \| Revenue concentration \| Medicaid and other government programs \| Connecticut
Concentrations
Concentrations (as a percent)	3.40%	5.00%	5.50%
Revenue \| Revenue concentration \| Medicaid and other government programs \| Kentucky
Concentrations
Concentrations (as a percent)	1.90%	2.30%	3.20%
Revenue \| Revenue concentration \| Medicaid and other government programs \| New York
Concentrations
Concentrations (as a percent)	1.10%	1.00%	1.70%
Revenue \| Revenue concentration \| Medicaid and other government programs \| Tennessee
Concentrations
Concentrations (as a percent)	3.10%	4.00%	1.70%
Revenue \| Revenue concentration \| Medicaid and other government programs \| Florida
Concentrations
Concentrations (as a percent)	0.60%	0.30%	0.90%
Revenue \| Revenue concentration \| Medicaid and other government programs \| Others
Concentrations
Concentrations (as a percent)	0.80%	0.10%	0.40%
Revenue \| Revenue concentration \| All other payors
Concentrations
Concentrations (as a percent)	5.10%	8.60%	6.10%
Accounts receivable \| Receivable concentration
Concentrations
Concentrations (as a percent)	100.00%	100.00%
Accounts receivable \| Receivable concentration \| Medicare program
Concentrations
Concentrations (as a percent)	62.60%	53.20%
Concentrations amount, gross	$ 96,464	$ 64,128
Accounts receivable \| Receivable concentration \| Medicaid and other government programs
Concentrations
Concentrations (as a percent)	22.80%	32.20%
Concentrations amount, gross	$ 35,175	$ 38,825
Accounts receivable \| Receivable concentration \| Medicaid and other government programs \| Ohio
Concentrations
Concentrations (as a percent)	6.10%	9.10%
Concentrations amount, gross	$ 9,341	$ 10,937
Accounts receivable \| Receivable concentration \| Medicaid and other government programs \| Connecticut
Concentrations
Concentrations (as a percent)	3.70%	5.60%
Concentrations amount, gross	$ 5,638	$ 6,735
Accounts receivable \| Receivable concentration \| Medicaid and other government programs \| Kentucky
Concentrations
Concentrations (as a percent)	2.20%	2.70%
Concentrations amount, gross	$ 3,444	$ 3,216
Accounts receivable \| Receivable concentration \| Medicaid and other government programs \| Wisconsin
Concentrations
Concentrations (as a percent)	2.30%	4.80%
Concentrations amount, gross	$ 3,549	$ 5,756
Accounts receivable \| Receivable concentration \| Medicaid and other government programs \| New York
Concentrations
Concentrations (as a percent)	2.10%	2.80%
Concentrations amount, gross	$ 3,229	$ 3,338
Accounts receivable \| Receivable concentration \| Medicaid and other government programs \| Tennessee
Concentrations
Concentrations (as a percent)	2.70%	3.10%
Concentrations amount, gross	$ 4,135	$ 3,741
Accounts receivable \| Receivable concentration \| Medicaid and other government programs \| Florida
Concentrations
Concentrations (as a percent)	2.20%	3.70%
Concentrations amount, gross	$ 3,416	$ 4,451
Accounts receivable \| Receivable concentration \| Medicaid and other government programs \| Others
Concentrations
Concentrations (as a percent)	1.60%	0.50%
Concentrations amount, gross	$ 2,423	$ 651
Accounts receivable \| Receivable concentration \| All other payors
Concentrations
Concentrations (as a percent)	14.50%	14.60%
Concentrations amount, gross	$ 22,402	$ 17,561
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)	62.00%	53.00%
Accounts receivable net of contractual allowances \| Medicaid and other government programs
Concentrations
Concentrations (as a percent)	24.00%	32.00%
Accounts receivable net of contractual allowances \| Self Pay
Concentrations
Concentrations (as a percent)	2.00%	1.00%
Accounts receivable net of contractual allowances \| Insurance
Concentrations
Concentrations (as a percent)	12.00%	14.00%
0-90 \| Accounts receivable net of contractual allowances
Concentrations
Concentrations (as a percent)	48.00%	49.00%
0-90 \| Accounts receivable net of contractual allowances \| Medicare program
Concentrations
Concentrations (as a percent)	31.00%	27.00%
0-90 \| Accounts receivable net of contractual allowances \| Medicaid and other government programs
Concentrations
Concentrations (as a percent)	11.00%	15.00%
0-90 \| Accounts receivable net of contractual allowances \| Self Pay
Concentrations
Concentrations (as a percent)	1.00%	1.00%
0-90 \| Accounts receivable net of contractual allowances \| Insurance
Concentrations
Concentrations (as a percent)	5.00%	6.00%
91-180 \| Accounts receivable net of contractual allowances
Concentrations
Concentrations (as a percent)	17.00%	20.00%
91-180 \| Accounts receivable net of contractual allowances \| Medicare program
Concentrations
Concentrations (as a percent)	13.00%	13.00%
91-180 \| Accounts receivable net of contractual allowances \| Medicaid and other government programs
Concentrations
Concentrations (as a percent)	3.00%	5.00%
91-180 \| Accounts receivable net of contractual allowances \| Insurance
Concentrations
Concentrations (as a percent)	1.00%	2.00%
181-365 \| Accounts receivable net of contractual allowances
Concentrations
Concentrations (as a percent)	20.00%	14.00%
181-365 \| Accounts receivable net of contractual allowances \| Medicare program
Concentrations
Concentrations (as a percent)	13.00%	8.00%
181-365 \| Accounts receivable net of contractual allowances \| Medicaid and other government programs
Concentrations
Concentrations (as a percent)	4.00%	4.00%
181-365 \| Accounts receivable net of contractual allowances \| Self Pay
Concentrations
Concentrations (as a percent)	1.00%
181-365 \| Accounts receivable net of contractual allowances \| Insurance
Concentrations
Concentrations (as a percent)	2.00%	2.00%
>1 yr. \| Accounts receivable net of contractual allowances
Concentrations
Concentrations (as a percent)	15.00%	17.00%
>1 yr. \| Accounts receivable net of contractual allowances \| Medicare program
Concentrations
Concentrations (as a percent)	5.00%	5.00%
>1 yr. \| Accounts receivable net of contractual allowances \| Medicaid and other government programs
Concentrations
Concentrations (as a percent)	6.00%	8.00%
>1 yr. \| Accounts receivable net of contractual allowances \| Insurance
Concentrations
Concentrations (as a percent)	4.00%	4.00%

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