Revenue Recognition - Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended
Apr. 03, 2021	Mar. 28, 2020
Disaggregation of Revenue
Consulting services revenues	$ 146,518	$ 126,158
United States
Disaggregation of Revenue
Consulting services revenues	117,247	100,740
United Kingdom
Disaggregation of Revenue
Consulting services revenues	23,286	19,066
Other
Disaggregation of Revenue
Consulting services revenues	5,985	6,352
Fixed-price
Disaggregation of Revenue
Consulting services revenues	33,433	28,988
Time-and-materials
Disaggregation of Revenue
Consulting services revenues	$ 113,085	$ 97,170

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

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