FAIR VALUE MEASUREMENT - Fair Value Measurement (Details) - USD ($) $ in Thousands | Jun. 27, 2021 | Dec. 27, 2020 | Jun. 28, 2020 | Dec. 29, 2019 |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | | |
Cash, cash equivalents, restricted cash and restricted cash equivalents | $ 159,670 | $ 118,612 | $ 141,840 | $ 92,371 |
Restricted investments classified as held-to-maturity | 140,302 | 158,296 | | |
Deferred compensation investments | 6,303 | 5,915 | | |
Municipal debt securities | | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | | |
Restricted investments classified as held-to-maturity | 63,926 | 70,723 | | |
Corporate debt securities | | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | | |
Restricted investments classified as held-to-maturity | 75,014 | 85,937 | | |
Agency mortgage-backed securities | | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | | |
Restricted investments classified as held-to-maturity | 267 | 512 | | |
U.S. government and agency securities | | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | | |
Restricted investments classified as held-to-maturity | 1,095 | 1,124 | | |
Fair value, recurring | Total fair value | | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | | |
Cash and cash equivalents | 105,234 | 62,507 | | |
Fair value, recurring | Total fair value | Restricted assets | | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | | |
Restricted cash and cash equivalents | 54,436 | 56,105 | | |
Cash, cash equivalents, restricted cash and restricted cash equivalents | 159,670 | 118,612 | | |
Restricted investments classified as held-to-maturity | 140,302 | 158,296 | | |
Deferred compensation investments | 6,303 | 5,915 | | |
Fair value, recurring | Total fair value | Restricted assets | Municipal debt securities | | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | | |
Restricted investments classified as held-to-maturity | 63,926 | 70,723 | | |
Fair value, recurring | Total fair value | Restricted assets | Corporate debt securities | | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | | |
Restricted investments classified as held-to-maturity | 75,014 | 85,937 | | |
Fair value, recurring | Total fair value | Restricted assets | Agency mortgage-backed securities | | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | | |
Restricted investments classified as held-to-maturity | 267 | 512 | | |
Fair value, recurring | Total fair value | Restricted assets | U.S. government and agency securities | | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | | |
Restricted investments classified as held-to-maturity | 1,095 | 1,124 | | |
Fair value, recurring | Quoted prices in active markets for identical assets (level 1) | | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | | |
Cash and cash equivalents | 105,234 | 62,507 | | |
Fair value, recurring | Quoted prices in active markets for identical assets (level 1) | Restricted assets | | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | | |
Restricted cash and cash equivalents | 54,436 | 56,105 | | |
Cash, cash equivalents, restricted cash and restricted cash equivalents | 159,670 | 118,612 | | |
Restricted investments classified as held-to-maturity | 0 | 0 | | |
Deferred compensation investments | 6,303 | 5,915 | | |
Fair value, recurring | Quoted prices in active markets for identical assets (level 1) | Restricted assets | Municipal debt securities | | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | | |
Restricted investments classified as held-to-maturity | 0 | 0 | | |
Fair value, recurring | Quoted prices in active markets for identical assets (level 1) | Restricted assets | Corporate debt securities | | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | | |
Restricted investments classified as held-to-maturity | 0 | 0 | | |
Fair value, recurring | Quoted prices in active markets for identical assets (level 1) | Restricted assets | Agency mortgage-backed securities | | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | | |
Restricted investments classified as held-to-maturity | 0 | 0 | | |
Fair value, recurring | Quoted prices in active markets for identical assets (level 1) | Restricted assets | U.S. government and agency securities | | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | | |
Restricted investments classified as held-to-maturity | 0 | 0 | | |
Fair value, recurring | Significant other observable inputs (level 2) | | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | | |
Cash and cash equivalents | 0 | 0 | | |
Fair value, recurring | Significant other observable inputs (level 2) | Restricted assets | | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | | |
Restricted cash and cash equivalents | 0 | 0 | | |
Cash, cash equivalents, restricted cash and restricted cash equivalents | 0 | 0 | | |
Restricted investments classified as held-to-maturity | 140,302 | 158,296 | | |
Deferred compensation investments | 0 | 0 | | |
Fair value, recurring | Significant other observable inputs (level 2) | Restricted assets | Municipal debt securities | | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | | |
Restricted investments classified as held-to-maturity | 63,926 | 70,723 | | |
Fair value, recurring | Significant other observable inputs (level 2) | Restricted assets | Corporate debt securities | | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | | |
Restricted investments classified as held-to-maturity | 75,014 | 85,937 | | |
Fair value, recurring | Significant other observable inputs (level 2) | Restricted assets | Agency mortgage-backed securities | | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | | |
Restricted investments classified as held-to-maturity | 267 | 512 | | |
Fair value, recurring | Significant other observable inputs (level 2) | Restricted assets | U.S. government and agency securities | | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | | |
Restricted investments classified as held-to-maturity | 1,095 | 1,124 | | |
Fair value, recurring | Significant unobservable inputs (level 3) | | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | | |
Cash and cash equivalents | 0 | 0 | | |
Fair value, recurring | Significant unobservable inputs (level 3) | Restricted assets | | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | | |
Restricted cash and cash equivalents | 0 | 0 | | |
Cash, cash equivalents, restricted cash and restricted cash equivalents | 0 | 0 | | |
Restricted investments classified as held-to-maturity | 0 | 0 | | |
Deferred compensation investments | 0 | 0 | | |
Fair value, recurring | Significant unobservable inputs (level 3) | Restricted assets | Municipal debt securities | | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | | |
Restricted investments classified as held-to-maturity | 0 | 0 | | |
Fair value, recurring | Significant unobservable inputs (level 3) | Restricted assets | Corporate debt securities | | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | | |
Restricted investments classified as held-to-maturity | 0 | 0 | | |
Fair value, recurring | Significant unobservable inputs (level 3) | Restricted assets | Agency mortgage-backed securities | | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | | |
Restricted investments classified as held-to-maturity | 0 | 0 | | |
Fair value, recurring | Significant unobservable inputs (level 3) | Restricted assets | U.S. government and agency securities | | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | | |
Restricted investments classified as held-to-maturity | $ 0 | $ 0 | | |