Revenue and Allowances - Disaggregation of Revenue (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2022	Jan. 01, 2022	Jan. 02, 2021
Disaggregation of Revenue
Consulting services revenues	$ 590,901	$ 565,933	$ 508,373
United States
Disaggregation of Revenue
Consulting services revenues	470,233	451,436	405,808
United Kingdom
Disaggregation of Revenue
Consulting services revenues	89,235	86,191	79,922
Other
Disaggregation of Revenue
Consulting services revenues	31,433	28,306	22,643
Fixed-price
Disaggregation of Revenue
Consulting services revenues	110,129	136,276	124,383
Time-and-materials
Disaggregation of Revenue
Consulting services revenues	$ 480,772	$ 429,657	$ 383,990

Amount, excluding tax collected from customer, of revenue from satisfaction of performance obligation by transferring promised good or service to customer. Tax collected from customer is tax assessed by governmental authority that is both imposed on and concurrent with specific revenue-producing transaction, including, but not limited to, sales, use, value added and excise.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
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Reference 2: http://www.xbrl.org/2003/role/disclosureRef
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+ Details