SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Property and Equipment (Details) - USD ($)	12 Months Ended
	Dec. 26, 2018	Dec. 27, 2017	Dec. 28, 2016
Property, Plant and Equipment [Line Items]
Impairment charges	$ 0	$ 0	$ 0
Equipment | Minimum
Property, Plant and Equipment [Line Items]
Useful life of asset	3 years
Equipment | Maximum
Property, Plant and Equipment [Line Items]
Useful life of asset	7 years
Furniture and fixtures | Minimum
Property, Plant and Equipment [Line Items]
Useful life of asset	3 years
Furniture and fixtures | Maximum
Property, Plant and Equipment [Line Items]
Useful life of asset	7 years
Computer equipment and software | Minimum
Property, Plant and Equipment [Line Items]
Useful life of asset	3 years
Computer equipment and software | Maximum
Property, Plant and Equipment [Line Items]
Useful life of asset	7 years
Leasehold improvements | Minimum
Property, Plant and Equipment [Line Items]
Useful life of asset	10 years
Leasehold improvements | Maximum
Property, Plant and Equipment [Line Items]
Useful life of asset	15 years
Landlord funded assets | Minimum
Property, Plant and Equipment [Line Items]
Useful life of asset	10 years
Landlord funded assets | Maximum
Property, Plant and Equipment [Line Items]
Useful life of asset	15 years