LEASES - Impact of Adoption (Details) - USD ($) $ in Thousands	3 Months Ended
	Apr. 03, 2020	Mar. 29, 2019	Dec. 27, 2019
Operating leases:
Right-of-use assets	$ 22,612		$ 22,297
Lease liability	$ 5,717		5,550
Operating Lease, Liability, Current, Statement of Financial Position [Extensible List]	Lease liability
Lease liability, less current portion	$ 18,051		18,411
Operating Lease, Liability, Noncurrent, Statement of Financial Position [Extensible List]	Lease liability, less current portion
Total lease obligations	$ 23,768		23,961
Operating Lease, Liability, Statement of Financial Position [Extensible List]	Total lease obligations
Finance leases (included in equipment and leasehold improvements, net):
Equipment and leasehold improvements, gross	$ 27,627		27,334
Accumulated depreciation and amortization	(14,490)		(15,283)
Total equipment and leasehold improvements, net	13,137		12,051
Finance lease obligations	421		375
Finance lease obligations, less current portion	242		191
Total lease obligations	$ 663		$ 566
Operating Leases	4 years 11 months 16 days		4 years 7 months 2 days
Finance Leases	1 year 8 months 19 days		1 year 5 months 19 days
Operating Leases, discount rate	4.60%		5.14%
Finance Leases, discount rate	4.52%		4.80%
Operating lease, rent expense	$ 1,900	$ 1,300
Equipment under finance lease
Finance leases (included in equipment and leasehold improvements, net):
Equipment and leasehold improvements, gross	2,122		$ 1,957
Accumulated depreciation and amortization	(1,418)		(1,291)
Total equipment and leasehold improvements, net	$ 704		$ 666