Summary of Significant Accounting Policies - Revenue by Vertical Market as Percentage of Total Revenue (Details)	3 Months Ended
	Mar. 27, 2020	Mar. 29, 2019
Concentration Risk [Line Items]
Total revenue	100.00%
Customer Concentration Risk [Member] | Sales Revenue, Services, Net [Member]
Concentration Risk [Line Items]
Total revenue	100.00%	100.00%
Technology Service Providers [Member] | Customer Concentration Risk [Member] | Sales Revenue, Services, Net [Member]
Concentration Risk [Line Items]
Total revenue	34.90%	32.70%
Manufacturing [Member] | Customer Concentration Risk [Member] | Sales Revenue, Services, Net [Member]
Concentration Risk [Line Items]
Total revenue	15.00%	16.90%
Financial Services [Member] | Customer Concentration Risk [Member] | Sales Revenue, Services, Net [Member]
Concentration Risk [Line Items]
Total revenue	14.20%	14.10%
Energy [Member] | Customer Concentration Risk [Member] | Sales Revenue, Services, Net [Member]
Concentration Risk [Line Items]
Total revenue	6.20%	4.60%
General Markets [Member] | Customer Concentration Risk [Member] | Sales Revenue, Services, Net [Member]
Concentration Risk [Line Items]
Total revenue	16.30%	15.50%
Healthcare [Member] | Customer Concentration Risk [Member] | Sales Revenue, Services, Net [Member]
Concentration Risk [Line Items]
Total revenue	13.40%	16.20%