Acquisitions (Details) (USD $) In Thousands, unless otherwise specified	9 Months Ended			1 Months Ended	9 Months Ended	1 Months Ended		3 Months Ended	9 Months Ended	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013 Customer lists/relationships [Member]	Aug. 31, 2013 Acton Marketing, LLC [Member]	Sep. 30, 2013 Acton Marketing, LLC [Member]	Aug. 31, 2013 Acton Marketing, LLC [Member] Customer lists/relationships [Member]	Jun. 30, 2013 VerticalResponse, Inc. [Member]	Sep. 30, 2013 VerticalResponse, Inc. [Member]	Sep. 30, 2013 VerticalResponse, Inc. [Member]	Sep. 30, 2013 VerticalResponse, Inc. [Member] Customer lists/relationships [Member]	Sep. 30, 2013 VerticalResponse, Inc. [Member] Internal-use software [Member]	Sep. 30, 2013 Small business distributors [Member]
Acquisitions [Line Items]
Payments for acquisitions, net of cash acquired	$ 48,114	$ 32,632		$ 4,095			$ 27,299					$ 16,720
Goodwill				1,459	1,459		18,735		18,735
Goodwill, purchase accounting adjustments								(2,190)
Acquired intangible assets			$ 13,000			$ 3,600				$ 9,400	$ 4,200
Acquired intangible assets useful life						5 years				9 years	4 years