Revenue and Allowances - Reserves for Variable Consideration and Credit Risk (Details) - USD ($) $ in Thousands	12 Months Ended
	Jan. 01, 2022	Jan. 02, 2021	Dec. 28, 2019	Dec. 29, 2018
Disaggregation of Revenue
Allowance for doubtful accounts	$ 500	$ 700
Roll forward of the variable consideration and allowances for accounts receivable
Balance at, beginning of year	3,595	3,838
Increases to reserves, net of recoveries	2,612	2,092
Amounts written off and foreign currency translation	(2,951)	(2,335)
Balance at, end of year	3,256	3,595	$ 3,838
Cumulative effect of a change in accounting principle	205,834	209,019	197,751	$ 196,472
Roll forward of the variable consideration and allowances for unbilled services
Balance at beginning of year	1,000	1,503
Increases to reserves, net of recoveries	7,574	6,847
Amounts written off and foreign currency translation	(7,210)	(7,350)
Balance at end of year	1,364	1,000	1,503
Accounts receivable allowances	(337)	(479)	47
Reimbursable expenses	64,532	61,661	54,871
Retained Earnings
Roll forward of the variable consideration and allowances for accounts receivable
Cumulative effect of a change in accounting principle	215,784	216,999	200,249	$ 186,229
Cumulative Effect Period of Adoption, Adjustment
Roll forward of the variable consideration and allowances for accounts receivable
Cumulative effect of a change in accounting principle			(203)
Cumulative Effect Period of Adoption, Adjustment | Retained Earnings
Roll forward of the variable consideration and allowances for accounts receivable
Cumulative effect of a change in accounting principle			(203)
Cumulative Effect Period of Adoption, Adjustment | Retained Earnings | ASC 326
Roll forward of the variable consideration and allowances for accounts receivable
Cumulative effect of a change in accounting principle			(200)
Selling, general and administrative expenses
Roll forward of the variable consideration and allowances for unbilled services
Accounts receivable allowances	$ 27	$ 227	$ 173