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DEBT OBLIGATIONS - Line of credit (Details) |  |  |  |  | 3 Months Ended | 12 Months Ended |  |
--- | --- | --- | --- | --- | --- | --- | --- | ---
Jun. 26, 2019 USD ($) item | Nov. 09, 2018 USD ($) | Oct. 01, 2018 USD ($) | Jan. 20, 2017 USD ($) | Sep. 27, 2019 USD ($) | Dec. 28, 2018 USD ($) | Dec. 27, 2019 USD ($) | Dec. 28, 2018 USD ($) | Dec. 29, 2017 USD ($) | Dec. 20, 2018 USD ($) | Oct. 10, 2018 USD ($)
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Borrowings under term loan facility and line of credit |  |  |  |  |  |  | $ 138,000,000 | $ 70,000,000 | $ 1,000,000 |  |
Composite interest rate |  |  |  |  |  |  | 3.70% |  |  |  |
Interest rate (as a percent) |  |  |  |  |  | 4.30% |  | 4.30% |  |  |
Interest and principal payments |  |  |  |  |  | $ 149,881 |  |  |  |  |
Unsecured notes payable |  |  |  |  |  | $ 1,500,000 |  | $ 1,500,000 |  |  |
Letter of credit issued |  |  |  |  |  |  | $ 2,700,000 |  |  |  |
Quarterly installments |  |  |  |  | $ 2,500,000 |  |  |  |  |  |
Utility Customer Agreement |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Interest rate (as a percent) |  |  |  |  |  |  |  |  |  | 4.332% |
Unsecured notes payable |  |  |  |  |  |  | 900,000 |  |  |  |
Amount committed to repay |  |  |  |  |  |  |  |  |  | $ 1,700,000 |
2019 Credit Agreement [Member] | BMO | Base rate | Federal Funds Effective Swap Rate |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Spread on floating interest rate (as a percent) | 0.50% |  |  |  |  |  |  |  |  |  |
2019 Credit Agreement [Member] | BMO | Base rate | LIBOR | Maximum |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Spread on floating interest rate (as a percent) | 1.00% |  |  |  |  |  |  |  |  |  |
2019 Credit Agreement [Member] | BMO | Base rate | LIBOR | Minimum |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Spread on floating interest rate (as a percent) | 0.125% |  |  |  |  |  |  |  |  |  |
2019 Credit Agreement [Member] | BMO | LIBOR | Base rate |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Spread on floating interest rate (as a percent) | 1.00% |  |  |  |  |  |  |  |  |  |
2019 Credit Agreement [Member] | BMO | LIBOR | Base rate | Maximum |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Spread on floating interest rate (as a percent) | 2.00% |  |  |  |  |  |  |  |  |  |
2019 Credit Agreement [Member] | BMO | LIBOR | Base rate | Minimum |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Spread on floating interest rate (as a percent) | 1.125% |  |  |  |  |  |  |  |  |  |
Term A Loan | BMO |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
The aggregate amount under the revolving line of credit | $ 100,000,000 |  |  |  |  |  |  |  |  |  |
Unamortized debt issuance costs |  |  |  |  |  |  | 700,000 |  |  |  |
Delayed Draw Term Loan Facility |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Maximum borrowing capacity | 50,000,000 |  |  |  |  |  |  |  |  |  |
Line of credit facility minimum borrowing under each tranche | $ 10,000,000 |  |  |  |  |  |  |  |  |  |
Annual amortization of debt (as a Percent) |  |  |  |  | 2.50% |  |  |  |  |  |
Delayed Draw Term Loan Facility | Maximum |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Number of borrowings | item | 5 |  |  |  |  |  |  |  |  |  |
Revolving Credit Facility |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Maximum borrowing capacity | $ 50,000,000 |  |  |  |  |  |  |  |  |  |
The aggregate amount under the revolving line of credit | $ 100,000,000 |  |  |  |  |  |  |  |  |  |
Revolving Credit Facility | BMO | Maximum |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Commitment fee (as a percent) | 2.00% |  |  |  |  |  |  |  |  |  |
Revolving Credit Facility | BMO | Minimum |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Commitment fee (as a percent) | 0.84% |  |  |  |  |  |  |  |  |  |
Delayed Draw Term Loan And Revolving Credit Facility |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Unamortized debt issuance costs |  |  |  |  |  |  | 800,000 |  |  |  |
Delayed Draw Term Loan And Revolving Credit Facility | BMO | Maximum |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Fee on unused commitments (as a percent) | 0.35% |  |  |  |  |  |  |  |  |  |
Delayed Draw Term Loan And Revolving Credit Facility | BMO | Minimum |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Fee on unused commitments (as a percent) | 0.15% |  |  |  |  |  |  |  |  |  |
2018 Credit Agreement [Member] | BMO | Base rate | Federal Funds Effective Swap Rate |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Spread on floating interest rate (as a percent) |  |  | 0.50% |  |  |  |  |  |  |  |
2018 Credit Agreement [Member] | BMO | Base rate | LIBOR | Maximum |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Spread on floating interest rate (as a percent) |  |  | 3.00% |  |  |  |  |  |  |  |
2018 Credit Agreement [Member] | BMO | Base rate | LIBOR | Minimum |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Spread on floating interest rate (as a percent) |  |  | 0.25% |  |  |  |  |  |  |  |
2018 Credit Agreement [Member] | BMO | LIBOR | Base rate |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Spread on floating interest rate (as a percent) |  |  | 1.00% |  |  |  |  |  |  |  |
2018 Credit Agreement [Member] | BMO | LIBOR | Base rate | Maximum |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Spread on floating interest rate (as a percent) |  |  | 4.00% |  |  |  |  |  |  |  |
2018 Credit Agreement [Member] | BMO | LIBOR | Base rate | Minimum |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Spread on floating interest rate (as a percent) |  |  | 1.25% |  |  |  |  |  |  |  |
Revolving Credit Facility Member Two |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Maximum borrowing capacity |  |  | $ 30,000,000 |  |  |  |  |  |  |  |
Revolving Credit Facility Member Two | BMO | Maximum |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Fee on unused commitments (as a percent) |  |  | 0.40% |  |  |  |  |  |  |  |
Revolving Credit Facility Member Two | BMO | Minimum |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Fee on unused commitments (as a percent) |  |  | 0.20% |  |  |  |  |  |  |  |
Delayed Draw Term Loan Facility Two [Member] | BMO |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Maximum borrowing capacity |  |  | $ 90,000,000 |  |  |  |  |  |  |  |
Delayed Draw Term Loan Facility Two [Member] | BMO | Maximum |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Commitment fee (as a percent) |  |  | 4.00% |  |  |  |  |  |  |  |
Delayed Draw Term Loan Facility Two [Member] | BMO | Minimum |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Commitment fee (as a percent) |  |  | 0.94% |  |  |  |  |  |  |  |
Term Loan 2018 [Member] | BMO |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Maximum borrowing capacity |  |  |  |  |  |  |  |  |  |  | $ 70,000,000
Borrowings under term loan facility and line of credit |  | $ 70,000,000 |  |  |  |  |  |  |  |  |
2017 Credit Agreement [Member] | BMO | Base rate | Federal Funds Effective Swap Rate |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Spread on floating interest rate (as a percent) |  |  |  | 0.50% |  |  |  |  |  |  |
2017 Credit Agreement [Member] | BMO | Base rate | LIBOR | Maximum |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Spread on floating interest rate (as a percent) |  |  |  | 1.00% |  |  |  |  |  |  |
2017 Credit Agreement [Member] | BMO | Base rate | LIBOR | Minimum |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Spread on floating interest rate (as a percent) |  |  |  | 0.25% |  |  |  |  |  |  |
2017 Credit Agreement [Member] | BMO | LIBOR | Base rate |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Spread on floating interest rate (as a percent) |  |  |  | 1.00% |  |  |  |  |  |  |
2017 Credit Agreement [Member] | BMO | LIBOR | Base rate | Maximum |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Spread on floating interest rate (as a percent) |  |  |  | 2.00% |  |  |  |  |  |  |
2017 Credit Agreement [Member] | BMO | LIBOR | Base rate | Minimum |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Spread on floating interest rate (as a percent) |  |  |  | 1.25% |  |  |  |  |  |  |
Revolving line of credit | BMO |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Maximum borrowing capacity |  |  |  | $ 35,000,000 |  |  |  |  |  |  |
Revolving line of credit | BMO | Maximum |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Fee on unused commitments (as a percent) |  |  |  | 0.35% |  |  |  |  |  |  |
Revolving line of credit | BMO | Minimum |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Fee on unused commitments (as a percent) |  |  |  | 0.20% |  |  |  |  |  |  |
Standby letter of credit sub-facility | BMO |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Maximum borrowing capacity |  |  |  | $ 10,000,000 |  |  |  |  |  |  |
Standby letter of credit sub-facility | BMO | Maximum |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Commitment fee (as a percent) |  |  |  | 1.50% |  |  |  |  |  |  |
Standby letter of credit sub-facility | BMO | Minimum |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Commitment fee (as a percent) |  |  |  | 0.94% |  |  |  |  |  |  |
Notes payable for IBM |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Interest rate (as a percent) |  |  |  |  |  | 4.656% |  | 4.656% |  |  |
Interest and principal payments |  |  |  |  |  |  |  | $ 6,315 |  |  |
Notes payable for IBM | Software Agreements |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Software cost |  |  |  |  |  |  |  | 200,000 |  |  |
Unsecured notes payable |  |  |  |  |  | $ 211,000 | $ 133,000 | $ 211,000 |  |  |

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