Revenue Recognition - Reserves for Variable Consideration and Credit Risk (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 28, 2019	Dec. 29, 2018	Dec. 30, 2017
Allowance for doubtful accounts	$ 400	$ 700
Roll forward of the variable consideration and allowances for accounts receivable
Balance at, beginning of year	3,764	5,252
Increases to reserves	2,926	3,675
Amounts written off	(2,866)	(5,173)
Effects of foreign currency translation	14	10
Balance at, end of year	3,838	3,764	$ 5,252
Roll forward of the variable consideration and allowances for unbilled services
Balance at beginning of year	415	704
Increases to reserves	5,548	4,755
Amounts written off	(4,467)	(5,042)
Effects of foreign currency translation	(7)	2
Balance at end of year	1,503	415	704
Reimbursable expenses	54,871	48,817	$ 41,465
Selling, general and administrative expenses
Roll forward of the variable consideration and allowances for accounts receivable
Amounts written off	$ (173)	$ (1,237)