Business Acquisition Business Acquisition (Narrative) (Details) (USD $)	12 Months Ended					3 Months Ended		12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2012 Other Acquisitions [Member]	Dec. 31, 2011 Data Haven Limited Buzz Networks Limited And C Infinity [Member]	Jun. 30, 2011 Protus Ip Solutions Inc [Member]	Mar. 31, 2011 Protus Ip Solutions Inc [Member]	Dec. 31, 2010 Protus Ip Solutions Inc [Member]	Dec. 31, 2010 Venali Inc [Member]	Dec. 31, 2012 Ziff Davis, Inc [Member]
Total consideration of transaction, net of cash acquired				$ 32,900,000	$ 3,800,000			$ 233,000,000		$ 200,436,000
Business Acquisition, Purchase Price Allocation, Goodwill Amount			195,633,000					164,498,000		112,882,000
Business Acquisition, Purchase Price Allocation, Goodwill, Expected Tax Deductible Amount			15,800,000							12,900,000
Business Acquisition, Cost of Acquired Entity, Cash Paid			247,913,000					207,345,000		163,100,000
Goodwill, Period Increase (Decrease)						400,000	4,900,000
Deferred income taxes	1,150,000	6,822,000	(541,000)						600,000
Business Acquisition, Purchase Price Allocation, Liabilities Assumed			29,200,000					25,600,000		28,800,000
Business Acquisition, Purchase Price Allocation, Noncontrolling Interest										8,600,000
Business Acquisition Contributed Total Revenue			9,700,000	16,900,000				6,200,000		9,700,000
Business Acquisition, Purchase Price Allocation, Assets Acquired (Liabilities Assumed), Net			277,100,000
Business Acquisition Contributed Net Income										$ 1,600,000