Acquisitions (Components Of Intangible Assets) (Details) (USD $) In Thousands, unless otherwise specified		3 Months Ended	12 Months Ended	3 Months Ended		12 Months Ended	3 Months Ended		12 Months Ended	3 Months Ended	12 Months Ended	3 Months Ended		12 Months Ended	3 Months Ended	12 Months Ended	3 Months Ended
	Nov. 09, 2012 Engage Pty Ltd. [Member]	Mar. 31, 2013 Customer Relationships	Dec. 31, 2012 Customer Relationships	Mar. 31, 2013 Customer Relationships [Member] Engage Pty Ltd. [Member]	Mar. 31, 2013 Non-compete Agreements [Member]	Dec. 31, 2012 Non-compete Agreements [Member]	Mar. 31, 2013 Non-compete Agreements [Member] Engage Pty Ltd. [Member]	Mar. 31, 2013 Patents	Dec. 31, 2012 Patents	Mar. 31, 2013 Trade-Name [Member]	Dec. 31, 2012 Trade-Name [Member]	Mar. 31, 2013 Trade-Name [Member] Engage Pty Ltd. [Member]	Mar. 31, 2013 Other	Dec. 31, 2012 Other	Mar. 31, 2013 Technology [Member]	Dec. 31, 2012 Technology [Member]	Mar. 31, 2013 Technology [Member] Engage Pty Ltd. [Member]
Business Acquisition [Line Items]
Intangible assets	$ 3,600			$ 2,661			$ 76					$ 95					$ 768
Weighted Average Amortization Period		3 years 6 months	3 years 6 months	48 months	1 year 2 months 12 days	1 year 2 months 12 days	12 months	11 years	11 years	2 years 8 months 12 days	2 years 8 months 12 days	12 months	3 years	3 years	3 years 9 months 18 days	3 years 9 months 18 days	36 months