Summary of Significant Accounting Policies - Revenue by Vertical Market (Details)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Revenue by vertical market as a percentage of total revenue
Total revenue	100.00%	100.00%	100.00%
Healthcare [Member]
Revenue by vertical market as a percentage of total revenue
Total revenue	31.40%	32.70%	29.60%
Technology Service Providers [Member]
Revenue by vertical market as a percentage of total revenue
Total revenue	27.90%	31.20%	34.30%
Financial Services [Member]
Revenue by vertical market as a percentage of total revenue
Total revenue	6.80%	6.10%	6.70%
Energy [Member]
Revenue by vertical market as a percentage of total revenue
Total revenue	6.10%	6.00%	6.00%
General Markets [Member]
Revenue by vertical market as a percentage of total revenue
Total revenue	27.80%	24.00%	23.40%