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		6 Months Ended
	Jun. 30, 2017	Jul. 01, 2016	Jun. 30, 2017	Jul. 01, 2016
Concentration Risk [Line Items]
Total revenue	100.00%	100.00%	100.00%	100.00%
Technology Service Providers [Member]
Concentration Risk [Line Items]
Total revenue	32.60%	34.40%	33.00%	34.70%
Manufacturing [Member]
Concentration Risk [Line Items]
Total revenue	26.00%	24.30%	25.80%	23.80%
Healthcare [Member]
Concentration Risk [Line Items]
Total revenue	17.40%	18.50%	17.10%	19.10%
Financial Services [Member]
Concentration Risk [Line Items]
Total revenue	7.90%	7.70%	7.90%	7.60%
Energy [Member]
Concentration Risk [Line Items]
Total revenue	4.70%	5.40%	4.90%	5.70%
General Markets [Member]
Concentration Risk [Line Items]
Total revenue	11.40%	9.70%	11.30%	9.10%