Summary of Significant Accounting Policies - Revenue by Vertical Market as Percentage of Total Revenue (Details) - Customer Concentration Risk [Member] - Sales Revenue, Services, Net [Member]	3 Months Ended
	Mar. 29, 2019	Mar. 30, 2018
Concentration Risk [Line Items]
Total revenue	100.00%	100.00%
Technology Service Providers [Member]
Concentration Risk [Line Items]
Total revenue	32.70%	33.10%
Manufacturing [Member]
Concentration Risk [Line Items]
Total revenue	16.90%	19.30%
Financial Services [Member]
Concentration Risk [Line Items]
Total revenue	14.10%	13.70%
Energy [Member]
Concentration Risk [Line Items]
Total revenue	4.60%	4.80%
General Markets [Member]
Concentration Risk [Line Items]
Total revenue	15.50%	13.80%
Healthcare [Member]
Concentration Risk [Line Items]
Total revenue	16.20%	15.30%