ORGANIZATION AND SIGNIFICANT ACCOUNTING POLICIES - Balance sheet (Details) - USD ($) $ in Thousands	Sep. 26, 2020	Dec. 28, 2019	Sep. 28, 2019
ASSETS
Prepaid expenses and other current assets	$ 14,069	$ 19,644
Property and equipment, net	75,355	82,610
Operating lease right-of-use assets	34,652	37,768
LIABILITIES AND STOCKHOLDERS’ EQUITY
Current operating lease liabilities	8,425	7,768
Current maturities of long-term debt	20,819	15,185
Long-term debt, net of current portion	215,823	281,715
Noncurrent operating lease liabilities	$ 37,679	$ 42,200
No. 2016-02
ASSETS
Prepaid expenses and other current assets			$ 14,133
Property and equipment, net			82,415
Operating lease right-of-use assets			38,650
LIABILITIES AND STOCKHOLDERS’ EQUITY
Accrued expenses and other current liabilities			37,325
Current operating lease liabilities			6,705
Current maturities of long-term debt			42,319
Long-term debt, net of current portion			253,692
Noncurrent operating lease liabilities			44,382
Other liabilities			7,326
As Previously Reported | No. 2016-02
ASSETS
Prepaid expenses and other current assets			13,303
Property and equipment, net			81,242
Operating lease right-of-use assets			0
LIABILITIES AND STOCKHOLDERS’ EQUITY
Accrued expenses and other current liabilities			38,220
Current operating lease liabilities			0
Current maturities of long-term debt			42,138
Long-term debt, net of current portion			252,694
Noncurrent operating lease liabilities			0
Other liabilities			18,044
Impact of Adoption | No. 2016-02
ASSETS
Prepaid expenses and other current assets			830
Property and equipment, net			1,173
Operating lease right-of-use assets			38,650
LIABILITIES AND STOCKHOLDERS’ EQUITY
Accrued expenses and other current liabilities			(895)
Current operating lease liabilities			6,705
Current maturities of long-term debt			181
Long-term debt, net of current portion			998
Noncurrent operating lease liabilities			44,382
Other liabilities			$ (10,718)