Fair Value of Financial Instruments (Details) - USD ($) $ / shares in Units, $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 26, 2020	Dec. 28, 2019	Sep. 26, 2020	Dec. 28, 2019
Fair Value of Financial Instruments
Contingent consideration liability	$ 11,579	$ 11,579	$ 13,480	$ 11,579
Summary of changes in contingent consideration liability
Beginning balance	11,579
Ending balance	13,480	11,579
Money market mutual funds
Fair Value of Financial Instruments
Fair value per share of CRA's money market mutual fund share holdings (in dollars per share)				$ 1.00
Recurring | Level 1
Fair Value of Financial Instruments
Total Assets			150	$ 150
Contingent consideration liability	0	0	0	0
Total Liabilities			0	0
Summary of changes in contingent consideration liability
Beginning balance	0
Ending balance	0	0
Recurring | Level 1 | Money market mutual funds
Fair Value of Financial Instruments
Cash and cash equivalents			150	150
Recurring | Level 2
Fair Value of Financial Instruments
Total Assets			0	0
Contingent consideration liability	0	0	0	0
Total Liabilities			0	0
Summary of changes in contingent consideration liability
Beginning balance	0
Ending balance	0	0
Recurring | Level 2 | Money market mutual funds
Fair Value of Financial Instruments
Cash and cash equivalents			0	0
Recurring | Level 3
Fair Value of Financial Instruments
Total Assets			0	0
Contingent consideration liability	11,579	6,197	13,480	11,579
Total Liabilities			13,480	11,579
Summary of changes in contingent consideration liability
Beginning balance	11,579	6,197
Remeasurement of acquisition-related contingent consideration	921	3,285
Accretion	980	2,097
Ending balance	$ 13,480	$ 11,579
Recurring | Level 3 | Money market mutual funds
Fair Value of Financial Instruments
Cash and cash equivalents			$ 0	$ 0