Fair Value of Assets and Liabilities - Assets Measured at Fair Value (Details) - USD ($) $ in Thousands	Sep. 25, 2021	Dec. 26, 2020
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Cash equivalents	$ 15,970	$ 73,461
Investments in equity securities	27,358	19,186
Mutual funds	14,711	13,249
Total	58,039	105,896
Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Cash equivalents	15,970	73,461
Investments in equity securities	27,358	19,186
Mutual funds	14,711	13,249
Total	58,039	105,896
Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Cash equivalents	0	0
Investments in equity securities	0	0
Mutual funds	0	0
Total	0	0
Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Cash equivalents	0	0
Investments in equity securities	0	0
Mutual funds	0	0
Total	$ 0	$ 0