Revenue Recognition - Disaggregation of Revenue (Details) - USD ($) $ in Thousands	12 Months Ended
Jan. 02, 2021	Dec. 28, 2019	Dec. 29, 2018
Disaggregation of Revenue
Consulting services revenues	$ 508,373	$ 451,370	$ 417,648
United States
Disaggregation of Revenue
Consulting services revenues	405,808	357,156	329,678
United Kingdom
Disaggregation of Revenue
Consulting services revenues	79,922	72,169	65,874
Other
Disaggregation of Revenue
Consulting services revenues	22,643	22,045	22,096
Fixed-price
Disaggregation of Revenue
Consulting services revenues	124,383	107,344	95,096
Time-and-materials
Disaggregation of Revenue
Consulting services revenues	$ 383,990	$ 344,026	$ 322,552

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 606
-SubTopic 10
-Section 50
-Paragraph 4
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=118956577&loc=SL49130543-203045

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=118956577&loc=SL49130545-203045

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration